1. Field of the Invention
This invention relates generally to a photo-CVD (chemical vapor deposition) apparatus and, more particularly, is directed to a photo-CVD apparatus utilizing a light and a reaction gas to deposit a thin film on a substrate.
2. Description of the Prior Art
FIG. 1 is a partially cross-sectional view illustrating one example of a prior art photo-CVD apparatus of this kind that is disclosed in Japanese laid-open patent application No. 60-53016.
Referring to FIG. 1, there is provided a gas reaction chamber 1 within which a substrate (sample) 2 on which a thin film is to be deposited by the photo-CVD process is supported on a susceptor 3. Upon operation, the substrate 2 is heated by a heater 4. Specifically, a light source 5 which irradiates, for example, ultraviolet rays is located within a light source compartment 6 that is formed on the gas reaction chamber 1. The ultraviolet rays from the light source 5 irradiate the substrate 2 through an ultraviolet ray transmission plate 7 which tightly shields a window opening 7A formed through the gas reaction chamber 1. The reaction gas is introduced through a gas opening 8 to the gas reaction chamber 1 and exhausted to the outside through a gas exhausting opening 9.
FIG. 2 is a partially cross-sectional view similarly illustrating another example of a prior art photo-CVD apparatus that is disclosed in Japanese Laid-Open Patent Application No. 60-30122. In FIG. 2, like parts corresponding to those of FIG. 1 are marked with the same references and will not be described in detail.
In FIG. 2, reference numeral 10 designates a flue for gas through which a gas supplied from a gas introduction opening 11 is sent to the gas reaction chamber 1 through gas nozzles 12 so as to remove a thin film on the plate 7. Reference numeral 13 designates a reflection plate for the light emitted from the light source 5 and located within the compartment 6.
In the photo-CVD reaction chamber 1, the temperature in the chamber 1 is beyond 200.degree. C. even if the pressure therein is the vacuum condition or atmospheric or normal atmospheric condition. Further, the light source 5 is generally made of an electrode discharge tube and this electrode discharge tube 5 is easily affected at its electrode portion by heat. Accordingly, when this electrode discharge tube 5 used as the light source is located within the gas reaction chamber 1, the ambient temperature thereof is raised so high that as shown in FIG. 1, in most cases, the light source 5 is placed within the light source compartment 6 formed outside the gas reaction chamber 1. Also, the gas reaction chamber 1 and the light source compartment 6 are partitioned by the light transmission plate 7 made of material such as a quartz glass or the like and the conditions of the light source compartment 6 are controlled by the forced-cooling system.
In the photo-CVD apparatus shown in FIG. 2, in order to prevent the reaction gas remaining in the gas reaction chamber 1 from being accumulated on the light transmission plate 7 as an undesired film, gas such as N.sub.2, Ar, He or the like (this kind of gas is not reacted with the reaction gas and does not absorb the light emitted from the light source 5) is introduced from the gas introduction opening 11 to the light transmission plate 7 so as to blow off the undesired film deposited on the light transmission plate 7. According to this prior art system, however, there is a possibility that because of the temperature within the gas reaction chamber 1, the flow of the gas and the like, the undesired film adheres to the light transmission plate 7 sooner or later and hence the intensity of the light emitted from the light source 5 to the gas reaction chamber 1 is lowered by such undesired film deposited on the light transmission plate 7. There is then a possibility that the photo-CVD process will not be carried out as it is expected originally.